Walking and Gait Analysis
Human movement is most simply and conveniently attained by walking which relies on being pain free and having good joint and muscle condition. Sufficient muscle power and full ranges of motion of the legs are necessary to have efficient gait. One legs acts as a mechanical support for the bodyweight whilst the other swings forward to take its place and become the supporting leg. The simplest division of gait is into stance and swing phases which describe the position each leg is in the stages of the gait.
The gait cycle is the name given to the process of passing through all the stages of gait until you come back to the starting point. For approximately ten percent of the gait cycle both feet are on the ground, with a single foot stance accounting for forty percent of the time. The swing phases make up the rest of the cycle as the leg comes through to be placed down again. Quicker walking reduces the length of time these phases last until we are running where there is no double support phase with both feet placed down simultaneously.
The stance and swing phases consist of a precise and repeatable series of movements during normal locomotion, with five different stages of stance phase. These are initial contact, loading response, mid stance, terminal stance and preswing, although initial contact is often referred to as heel strike. Heel strike is a slight misnomer as some people do not heel strike or at least weight transfer to the heel later in the phase. Heel strike allows shock reduction and maintenance of stability and speed whilst accomplishing weight transfer to a new leg.
With one leg supporting the bodyweight the other limb is going through the swing phase. The body moves the centre of support over the foot in what is known as mid stance, the initial part of the phase of single leg support. Terminal stance occurs next as the heel of the supporting foot rises from the ground and finishes as the other leg makes heel strike and begins to support weight. Preswing is really a preparation for the swing phase and begins with the last part of the both leg support phase, finishing when the foot is raised to begin swing. Foot clearance above the ground and the forward motion of the leg to engage another step are the function of the swing phases of initial, mid and terminal swing phases.
Efficient gait includes aspects of shock absorption and energy conservation and alterations of joint movement or absence of muscle power may increase the joint contact forces which can lead to pathological changes in the structures abnormally loaded. Almost 60% of the body weight is transferred to the early stance leg in very short period, under 20 milliseconds.
This sudden loading is damped down by the joints of the leg which absorb and control the shock. As the foot initially contacts the ground the forces tend to bend the knee and this is resisted by straightening the knee which increases the forces suffered. Eccentric actions by the quadriceps at the knee and the adductors at the hip minimise some of the loading forces as the leg takes the weight.
The energy demands of walking are significant but not large in normal adults who walk at their own speed on the level and we choose our typical walking speed to minimise the energy expenditure. Walking speeds are always slowed down when a patient suffers from neurological and musculoskeletal conditions but because the gait cycle is slowed down in these cases the energy expenditure per unit time may not be increased. However, in stroke for example, the energy demand for accomplishing a specific distance can rise markedly, to more than three times the normal level.
Using a wheelchair cuts energy requirements per distance by 50% and allows speed to be maintained. The choice of using a wheelchair may be made by a patient when the amount of energy to get across a certain distance exceeds a certain level, often when the load exceeds 300% of what would be normally required.